An ultrahigh-precision processing called EEM (Elastic Emission Machining) of finishing the surface of a workpiece by bringing fine particles into contact with the processing face of a workpiece under almost no load while making a processing liquid containing dispersed fine particles flow along the processing face thereof and removing the atoms on the processing face to the depth at the order of atom by the interaction (like chemical bonding) between the fine particles and the processing face was developed by the inventors and has been already known. It was possible to perform two-dimensional synthetic-mirror light condensation to the world-smallest condensation spot of 90 nm×180 nm on a 1-km beam line in a large-scale photoradiation facility (SPring-8), by using two X-ray elliptical mirrors prepared by final finishing of X-ray elliptical mirrors of silicon single crystal by using the EEM method. Currently, a processing precision allowing beam condensation into a further smaller spot is obtained.
Patent Document 1 discloses a polishing machine for processing the polishing surface of a workpiece by bringing a revolving elastic material closer to the polishing surface of a workpiece immersed in a processing liquid containing fine particles uniformly dispersed and allowing the processing liquid to flow between them, the polishing machine comprising a rotation drive mechanism of rotating the workpiece and a feed mechanism of adjusting the relative position of the rotation drive mechanism and the revolving elastic material in the direction perpendicular to the rotation axis of the rotation drive mechanism. The elastic rotor used is a ball or cylinder of polyurethane. Alternatively, Patent Document 2 discloses a processing machine allowing reliable processing of a workpiece by using the same processing principle.
Yet alternatively, Patent Document 3 proposes a processing method of advancing processing by placing a workpiece and a high-pressure nozzle at a particular distance in a processing tank mainly containing ultrapure water, generating high-speed shearing stream of ultrapure water by ejection from the high-pressure nozzle placed in the area close to the surface of the workpiece, supplying fine particles chemically reactive with the workpiece onto the workpiece surface in the ultrapure water stream, and thus, removing the workpiece surface atoms chemically bound to the workpiece with the fine particles ejected in the high speed shearing stream.
The EEM is a processing method using the phenomenon that, when fine particles having a particle diameter of 10 nm to 10 μm are used and the fine particles and the workpiece surface atoms are bound to each other by chemical interaction, the surface atoms bound to the fine particles have back bonds lowered in strength, and are also removed when the fine particles are removed from the workpiece surface. Because the fine particles are forced to flow along the surface of the workpiece in EEM, microprojections on the workpiece surface are removed selectively, giving a smoothened surface having a surface roughness of 0.1 nm RMS (Root mean square). Factors having a large influence on processability in EEM include the combination of workpiece and fine particles, the surface state of workpiece, the shape and form of fine particles, and the like. For ultrahigh-precision processing, the surface state of the workpiece should be uniform, and the properties of the fine particles are also desirably uniform.
However, although it is possible to perform ultrahigh-precision processing of uniform materials such as silicon single crystal, the surface roughness of the workpieces having irregular surface such as materials having both fine crystalline and non-crystalline regions may be increased to 1 nm RMS or more, on the contrary, in the EEM processing. For example, ZERODUR® (SCHOTT AG), which is superior in shape stability in a wide temperature range and thus has been used as a substrate for high-precision mirror for use in various optical systems, belongs to glass-ceramic composite materials (hereinafter, referred to as “glass ceramics”) and contains both non-crystalline (amorphous) and crystalline compositions, and thus, if EEM is used directly for the processing of the material, it is quite difficult to achieve the surface smoothness at a surface roughness of 0.1 nm RMS or less, because the processing rate varies according to the crystal structure.    Patent Document 1: Japanese Examined Patent Publication No. 7-16870    Patent Document 2: Japanese Patent No. 3630987    Patent Document 3: Japanese Unexamined Patent Publication No. 2000-167770